1. Field of the Invention
The present invention relates to a discrete semiconductor device. More particularly, it relates to a discrete semiconductor device for small signal operation having excellent high-frequency characteristics and heat dissipation performance.
2. Description of the Related Art
A discrete semiconductor device of the prior art is typically packaged in a DIP (dual inline package) shown in FIG. 25. FIG. 25A is a cut-away view from above of a resin-sealed DIP, and FIG. 25B is a cut-away view of the side of the resin-sealed DIP. In the drawing, numeral 2 denotes a sealing resin, 8 denotes a discrete semiconductor element, 9 denotes a wire connecting an electrode of the discrete semiconductor element 8 and an inner lead 39, 38 denotes an island for securing the discrete semiconductor element 8, 39 denotes the inner lead and 40 denotes an outer lead.
In the case of such a resin-molded DIP, the discrete semiconductor element 8 is secured onto the island 38 of a lead frame 41 by die bonding and the electrode of the discrete semiconductor element 8 is connected to the inner lead 39 by means of the Au wire 9, then the circuit is sealed with resin by using an independent die for each discrete semiconductor element 8, with the lead being cut off the lead frame 41 thereby to fabricate the discrete semiconductor device (FIG. 27).
When packaging the discrete semiconductor device on a mother board, there has been such a problem that a large packaging area is required to connect the device to the mother board by using the outer lead 40 which is installed on a side face of the package and extends outward.
Also because the discrete semiconductor element and the mother board are connected by means of a lead, wiring length becomes longer and causes a substantial loss in the discrete semiconductor element in high-frequency region which leads to unsatisfactory high frequency characteristics.
Moreover, because the discrete semiconductor element is sealed with a resin of low thermal conductivity, heat dissipation efficiency decreases and causes such a problem that it is impossible to package discrete semiconductor elements of high power.
For example, Japanese Patent Kokai Publication No. 8-236665 discloses a method of packaging electronic elements on a mother board by means of bumps provided on the back of a resinsealed semiconductor device which carries an IC chip mounted thereon, without using leads.
However, because the discrete semiconductor element employs a high power element such as power MOS device compared to an IC which employs a low power element, heat transfer through the bumps is not enough to dissipate the heat generated by the semiconductor device and the like. Also when high-frequency elements are used, it has been necessary to improve the high-frequency characteristics by making the distance between the electrode of the high-frequency element and the mother board whereon the high-frequency element is mounted as short as possible.
Moreover, in the process of producing resin-sealed discrete semiconductor devices of the prior art, semiconductor elements are sealed with resin by using an independent die for each discrete semiconductor device and injecting the sealing resin in each die, although such a method requires it to fabricate a new die every time the external dimension or profile of the semiconductor divide is changed, thus making it difficult to reduce the period of time and cost of development of the semiconductor devices.
Also when a lead frame is used, peripheral portion of the frame except for the leads becomes unnecessary making it difficult to reduce the producing cost.